Flowserve 3200MD - Manual (Page 13)

User Instructions - Digital Positioner 3200MD LGENIM0059-09 12/13
13
 WARNING: Never connect a voltage source directly across
the positioner terminals. This could cause permanent
circuit board damage.
Determine if the loop will support the Logix 3200MD digital posi-
tioner by performing the following calculation.
Voltage = Compliance Voltage (@Current
max
) –
Current
max
• (R
barrier
+R
wire
)
Equation 1
The calculated voltage must be greater than 10 VDC in order to
safely support the Logix 3200MD digital positioner.
Example:
DCS Compliance Voltage = 19 VDC
R
barrier
= 300 Ω
R
wire
= 25 Ω
Current
max
= 20 mA
Voltage = 19 VDC – 0.020 A • (300 Ω + 25 Ω) = 12.5 VDC
The voltage 12.5 VDC is greater than the required 10.0 VDC; there-
fore, this system will support the Logix 3200MD digital positioner.
The Logix 3200MD positioner has a worst case input resistance
equivalent to 500 Ω at a 20 mA input current.
6.4 Cable Requirements
The Logix 3200MD digital positioner utilizes the HART Commu-
nication protocol. This communication signal is superimposed
on the 4-20 mA current signal. The two frequencies used by the
HART protocol are 1200 Hz and 2200 Hz. In order to prevent
distortion of the HART communication signal, cable capacitance
and cable length restrictions must be calculated. The cable length
must be limited if the capacitance is too high. Selecting a cable
with lower capacitance/foot rating will allow longer cable runs.
In addition to the cable capacitance, the network resistance also
affects the allowable cable length.
+
-
R
barrier
(if present) R
wire
Current
Source
Compliance
Voltage
Logix
3200IQ
Current
10
VDC
Figure 7: Compliance Voltage